Digestion catalyst



J. A. GILLIS DIGESTION CATALYST Original Filed May 7, 1964 IIL SODIUM SULFATE ADMIX COPPER SELENITE BUMPING mmsn'on a BINDER BLEND DIVIDE INTO MEASURED AMOUNTS a PACKAGE FIG. 4

INVENTOR. JOHN A. GILL/S BY Z 7 HTTORNEV Aug. 8, 1967 United States Patent 3,335,097 DIGESTION CATALYST John A. Gillis, Minneapolis, Minn., assignor to The Pillsbury Company, Minneapolis, Minn., a corporation of Delaware Continuation of application Ser. No. 365,700, May 7, 1964. This application Dec. 21, 1966, Ser. No. 605,126

7 Claims. (Cl. 252-428) This application is a continuation of Ser. No. 365,700, filed May 7, 1964, and now abandoned.

This invention relates to catalyst compositions and more particularly to an improved digestion catalyst. The invention is particularly useful in conducting Kjeldahl nitrogen determination tests.

There is wide recognition of the fact that the Kjeldahl nitrogen determination method is a complicated and timeconsuming procedure. Briefly, the Kjeldahl nitrogen determination method refers to the decomposition of organic material containing aminoid nitrogen by digestion of the sample with sulfuric acid in the presence of suitable catalysts to yield ammonium sulfate quantitatively. Ammonia is liberated from the ammonium sulfate with a non-volatile alkali and distilled into a known volume of a standard acid, the excess of which is then determined by acidimetry. The procedure is particularly objectionable when run on a large-scale basis over an extended period of time. One of the most disagreeable operations to be performed in conducting the test is the preparation of the catalyst which in the past, involved mixing several toxic substances. Some of these substances are harmful if brought into contact with the skin and produce a toxic dust which can contaminate the air.

Some objections to the procedure have been overcome by placing the catalyst in a digestible container such as a small plastic bag or packet. In the last few years these packets have come into relatively wide-spread use by laboratories where Kjeldahl determinations are conducted on a large-scale basis.

The catalyst packets of the type described do, however, have certain shortcomings. One shortcoming is that the time required for the package to break open has been excessive thus slowing the test. Another disadvantage of the prior art is that the catalyst has been relatively slow acting even after the packet has opened. Yet another disadvantage of the prior art is the fact that there is a toxicity hazard present during the preparation of the packet, largely due to dusting of the catalyst materials. It was also found that the ratio of the various catalyst materials sometimes varied from one packet to another even though the catalyst materials were carefully mixed before packaging. This is believed to be due to uneven settling or Stratification of the several catalyst materials in the various mechanical apparatuses which in practice must be employed for handling the mixture between the time the ingredients are mixed together and the packaging operation is completed. This phenomenon, referred to herein as stratification, can cause the composition to vary from one catalyst package to the next thereby reducing the reliability of an otherwise carefully controlled test.

In view of these and other deficiencies of the prior art, it is one object of this invention to provide an improved, prepackaged digestion catalyst which will effectively speed up the digestion time required in conducting Kjeldahl nitrogen determination tests.

Yet another object of the invention is the provision of an improved Kjeldahl nitrogen determination catalyst which can be prepared with a minimum toxicity hazard.

Yet another object of the invention is the provision of an improved packaged Kjeldahl nitrogen determination catalyst wherein the ratio of catalyst ingredients in each 3,335,097 Patented Aug. 8, 1967 package can be reliably maintained within predetermined limits.

Still another object of the invention is the provision of an improved Kjeldahl nitrogen determination catalyst wherein the package will be digested in less time than required heretofore.

Still another object of the invention is the provision of an improved Kjeldahl nitrogen determination catalyst which will inhibit excessive foaming during the digestion operation.

Other more detailed and specific objects will be apparent from the accompanying specification and drawings wherein the same numerals refer to corresponding parts in the several .views and wherein:

FIGURE 1 is a plan view of a packet embodying the present invention;

FIGURE 2 is a transverse vertical sectional view taken along line 2-2 of FIG. 1;

FIGURE 3 is a greatly enlarged view of the catalyst according to the invention as it appears when observed under the microscope; and

FIGURE 4 is a flow chart illustrating the steps performed in preparing and packaging the catalyst of the invention.

Briefly stated, in accordance with the preferred formof the invention, the catalyst comprises a major proportion of an alkali metal sulfate such as sodium sulfate, a relatively minor amount of copper selenite, a non-reactive particulate material to prevent bumping, and a minor amount of an agglomerating binder material to prevent stratification of the catalyst materials during preparation enclosed in a digestible container. In accordance with one preferred form of the invention, the non-reactive particulate material comprises ground pumice and the binder material comprises an oil such as mineral oil in an amount sufiicient to agglomerate the solid components of the catalyst.

Referring now to the drawings, there is shown in FIG- URES 1 and 2 a catalyst packet 10 in accordance with the present invention. The packet 10 is composed of a thin-walled container or tube 12 of a material such as an organic resin which is digestible in sulfuric acid. One

example of such a resin is polyethylene. While various resins can be employed, they should, of course, contain no nitrogen. At the upper and lower ends of the packet 10, the tube 12 is sealed along parallel, transverse seal lines '14 and 16. The seals 14 and 16 are conveniently prepared with conventional heat-sealing equipment or other suitable means after the packet 10 has been filled.

It was found that the thickness of the wall of the tube 12 had an important bearing upon the time required for digestion which, of course, should be minimized. It was discovered that by employing a polyethylene film from about .0005 to about .0015 inch in thickness, the time required for the packet to open was substantially reduced by comparison with the results obtained in the prior art. For example, it Was found that by employing a polyethylene film of from .001 inch thickness, the time required for the catalyst packet to open after placement in the Kjeldahl flask was from about Sto 4 minutes less than that required in the case of a polyethylene film having a thickness of .002 inches. It was also surprising to find there a a relatively minor amount of copper selenite, a non-reactive particulate material to prevent bumping, and a minor amount of a binder material to prevent Stratification of the catalyst materials during preparation. In accordance with one preferred form of the invention, the non-reactive particulate material comprises finely ground pumice. The

some stratification will take place which, of course, is undesirable. The amount of pumice to be employed will depend upon the amount required to effectively prevent violent or unsteady boiling. It was found that from about liquid binder material comprises an oil such as mineral 5 .5 to 2 parts of pumice by weight for each 100 parts by oil in an amount sufficient to agglomerate components of Weight of sodium sulfate will be effective. In one preferred the catalyst. form of the invention, one part by weight of pumice is Referring now to FIGURE 3 which illustrates the catused for each 100 parts by weight of sodium sulfate. alyst as it appears under a microscope, there are shown As described hereinabove, the preferred binder material three agglomerated masses or granules each indicated comprises a nonvolatile, nitrogen-free liquid with sufiigenerally at 20. The granules 20 each include sodium sulcient tack to hold the particles from which the catalyst fate particles 22, copper selenite particles 24, a non-reacis formed together in aggregated masses. While any of a tive particulate bumping inhibitor material such as pumice variety of nitrogen-free oily materials can be employed, 26 and a nonvolatile liquid binder 28. As shown in the I prefer to employ a heavy-duty mineral oil having a visfigure, the granules 20 are of various sizes. The binder cosity of about 150 to 200 Saybolt seconds and prefermaterial 28 coats most of the particles and completely ably between 170 and 180 Saybolt seconds. Generally encapsulates many of the finer particles which would form speaking, less viscous oils must be used in greater amounts a dust in the absence of the binder. It can also be seen to provide the same agglomerating effect. On the other that the binder holds the various component materials hand, the binder should not be so viscous as to prevent of the catalyst together so as to prevent stratification and 20 the particulate materials of the catalyst from becoming the resultant likelihood that in the absence of the binder coated. The minimum amount of binder which can be the different catalyst materials would be present in difused is determined by the quantity required to prevent ferent amount in different packets. Stratification of the dry ingredients by agglomerating the The amount of sodium sulfate to be used in each packet particles together. If too much of the binder material is depends upon the particular test procedure being followed. present, the catalyst will not be free flowing and con- In many of the standard Kjeldahl tests, such as test method sequently diflicult to measure and fill into the packets and 4611 of the American Association of Cereal Chemists, also may remain in the form of lumps after the packet has 10 grams of the alkali metal sulfate is employed for every been digested thereby increasing the time required for the one gram of sample material which is to be tested (potascatalyst to become effective in the reaction. It was found sium sulfate in the case of the AACC test). In other stand- 30 that from about .5 to 2 parts by weight of mineral oil ard tests, different amounts of the alkali metal sulfate can binder should be used for each 100 parts by weight of be employed. Greater amounts are usually required when sodium sulfate. About .75 parts. by weight of binder for a greater volume of protein material is to be tested. each 100 parts by weight of sodium sulfate was effective Concerning the amount of copper selenite to use, enough when heavy-duty mineral oil was used as a binder. should be present to provide a satisfactory digestion speed The process employed for forming the packet as set as indicated by the time required for the solution to beforth hereinabove will now be described by reference to come clear. If excessive amounts of copper selenite are FIGURE 4. To begin the operation, sodium sulfate is employed, there may be a loss through the neck of the placed in a suitable mixing vessel. To this vessel is mixed Kjeldahl flask. For most purposes, from about 1 to 3 copper selenite, the bumping inhibitor material and the parts by weight of copper selenite can be employed for binder. The materials are then thoroughly blended until each 100 parts by weight of sodium sulfate. In a preferred a uniform, homogeneous and flowable mixture is proform of the invention, about 2 parts by weight of copper duced. As blending is accomplished, the binder will coat selenite are employed for each 100 parts by weight of most of the particulate material and bind the particles sodium sulfate. together to form the agglomerated masses 20. The blended Among the advantages of the invention is the time material is then divided into measured quantities and saving made possible through the use of copper selenite. packaged in the packets 10 by using any suitable and In a typical test, 12 minutes is saved for each analysis well-known packaging machine or by hand. in an 18% protein composition. For a lower protein The invention will be better understood by reference concentration, even greater time can be saved. In a comto the examples set forth in Table I below, it being underposition containing less protein, even more time can be stood that after the packets have been formed, they are saved in most cases in comparison with a catalyst compoeach used in performing the Kjeldahl nitrogen determinasition which includes no copper selenite. However, betion test substantially as set forth hereinbelow.

TABLE I Example Potassium sulfate 100 100 100 Sodium sulfate 100 100 100 100 100 100 100 Copper selenite 1 1 1 3 3 3 2 2 2 2 1 Light mineral oil, U.S.P 1 1 1 2 Heavy mineral oil, Say. Secon 79 79 .2 2 79 75 75 Polyethylene packet, thickness, .0005 x x x x Polyethylene packet, thickness, .0015 in x x x Polyethylene packet, thickness, .001 in x x x x Pumice (fine, FF grade) .5 .5 1 5 1 5 5 Pumice (coarse). .5 1 2 1 All amounts given are parts by weight.

cause of the high toxicity of copper selenite, in the past it has been difiicult to handle and sometimes unsafe to use.

The preferred form of non-reactive particulate bumping inhibitor is finely divided pumice. While extra fine (FF grade) is preferred, other grades such as fine or coarse can be used. If relatively large particles are used,

The following Kjeldahl nitrogen determination test is set forth by way of example. To begin the test, one gram of flour or other protein-containing substance is transferred to a Kjeldahl flask. The catalyst packet according to the invention is then inserted into the flask and 25 ml. concentrated sulfuric acid is added. Digestion is then carried out by boiling for a period of 45 minutes on a 500 watt digestion heater. After digestion, the flask is removed and cooled, but the contents are not allowed to crystallize. About 300 ml. of water and 70 ml. of concentrated sodium hydroxide are, then added. The flask is placed on a distillation rack until 150 to 200' ml. of distillate is collected. The distillate is collected in a beaker containing 60 ml. of 4% boric acid solution containing an indicator such as Methyl Purple. The distillate is then titrated past grey color to the first light purple color with .1253 N sulfuric acid. The number of milliliters of acid used is reported directly as the percentage of protein present in the flour sample. For other materials, a special factor for protein conversion must be used.

While the invention is described in connection with a preferred embodiment thereof, it will be understood that it is not intended to limit the invention thereto but rather it is intended to cover all alternative constructions and modifications falling within the spirit and scope of the appended claims.

I claim:

1. An agglomerated granular free-flowing protein digestion catalyst for conducting Kjeldahl protein determination tests, said catalyst comprising:

(a) a major proportion of sodium sulphate present in particulated form,

(b) a finely divided bumping inhibitor in an amount suflicient to prevent uncontrolled boiling during the performance of said Kjeldahl determination,

(c) an effective amount of copper selenite present in particulated form,

(d) a binder comprising a nitrogen-free non-volatile and normally tacky liquid in an amount sufficient to cause the particles to adhere to one another and form free-allowing agglomerates, and

(e) a container enclosing said catalyst comprising a thin film of .a nitrogen-free resinous sheet material soluble in sulphuric acid.

2. An agglomerated granular free-flowing protein digestion catalyst for conducting Kjeldahl protein determination tests, comprising:

(a) a package comprising a thin film of polyethylene sheet material enclosing said catalyst and said catalyst comprising:

(b) a major proportion of sodium sulphate present in particulated form,

(c) a finely divided bumping inhibitor in an amount sufiicient to prevent uncontrolled boiling during the performance of said' Kjeldahl determination,

(d) an effective amount of copper selenite present in particulated form, and

(e) a binder comprising a nitrogen-free non-volatile and normally tacky liquid in an amount sufiicient to cause the particles to adhere to one another and form free-flowing agglomerates.

3. An agglomerated granular free-flowing protein digestion catalyst for conducting Kjeldahl protein determination tests, said catalyst comprising:

(a) a major proportion of sodium sulphate present in particulated form,

(b) from about 1 to 3 parts by weight of copper selenite for each 100 parts by weight of sodium sulphate,

(c) a binder comprising a nitrogen-free non-volatile and normally tacky liquid in an amount suflicient to cause the particles to adhere to one another and form free-flowing agglomerates, and

(d) a package enclosing said catalyst comprising a thin film of a nitrogen-free resinous sheet material soluble in sulphuric acid.

4. An agglomerated granular free-flowing protein digestion catalyst for conducting Kjeldahl protein determination tests, said catalyst comprising:

(a) a major proportion of sodium sulphate present in particulated form,

(b) from about 1 to 3 parts by weight of copper selenite for each parts by Weight of sodium sulphate,

(c) a relatively small amount of pumice present in particulated form,

(d) a binder comprising a nitrogen-free non-volatile and normally tacky liquid in an amount suificient to cause the particles to adhere to one another andform free-flowing agglomerates, said binder comprising essentially of a heavy duty mineral oil present in the amount of from about .2 to 2 parts by weight for each 100 parts by weight of sodium sulphate, and

(e) a package enclosing said catalyst comprising a thin film of a nitrogen-free resinous sheet material soluble in sulphuric acid.

5. A packaged free-flowing granular agglomerated protein digestion catalyst for conducting Kjeldahl nitrogen protein determinations consisting essentially of:

(a) a major proportion of particulated sodium sulphate,

(b) about 1 to 3 parts by weight of copper selenite for each 100 parts by Weight of sodium sulphate,

(c) from about .5 to 2 parts by weight of granulated pumice for each 100 parts by weight of sodium sulphate,

(d) a non-volatile, nitrogen-free binder formed from a tacky nitrogen-free liquid present in the amount of from about .2 to 2 parts by weight for each 100 parts by weight of sodium sulphate, and

(e) a package enclosing the catalyst, said package comprising a thin film of nitrogen-free resinous sheet material soluble in sulphuric acid.

6. An agglomerated granular free-flowing protein digestion catalyst for conducting Kjeldahl protein determination tests, said catalyst comprising:

(a) a major proportion of alkali metal sulphate present in particulated form,

(b) a finely divided bumping inhibitor in an amount sufiicient to prevent uncontrolled boiling during the performance of said Kjeldahl determination,

(c) an efiective amount of copper selenite present in particulated form,

(d) a binder comprising a nitrogen-free non-volatile and tacky material in an amount sufficient to cause the particles to adhere to one another and form freeflowing agglomerates, and

(e) a container enclosing said catalyst comprising a thin filmof a nitrogen-free resinous sheet material soluble in sulphuric acid.

7. The agglomerated granular free-flowing protein digestion catalyst of claim 6 wherein said alkali metal sulphate comprises potassium sulphate.

References Cited UNITED STATES PATENTS 2,820,699 1/1958 Morris 23-230 OTHER REFERENCES Copper Selenite as a Catalyst in the Kjeldahl Nitrogen Determination, Journal of Biological Chemistry, vol. 113, pages 749' to 751 (1931).

DANIEL E. WYMAN, Primary Examiner.

L. G. XIARHOS, Assistant Examiner. 

6. AN AGGLOMERATED GRANULAR FREE-FLOWING PROTEIN DIGESTION CATALYST FOR CONDUCTING KJELDAHL PROTEIN DETERMINATION TESTS, SAID CATALYST COMPRISING: (A) A MAJOR PROPORTION OF ALKALI METAL SULPHATE PRESENT IN PARTICULATED FORM, (B) A FINELY DIVIDED BUMPING INHIBITOR IN AN AMOUNT SUFFICIENT TO PREVENT UNCONTROLLED BOILING DURING THE PERFORMANCE OF SIAD KJELDAHL DETERMINATION, (C) AN EFFECTIVE AMOUNT OF COPPER SELENITE PRESENT IN PARTICULATED FORM, (D) A BINDER COMPRISING A NITROGEN-FREE NON-VOLATILE AND TACKY MATERIAL IN AN AMOUNT SUFFICIENT TO CAUSE THE PARTICLES TO ADHERE TO ONE ANOTHER AND FORM FREEFLOWING AGGLOMERATES, AND (E) A CONTAINER ENCLOSING SAID CATALYST COMPRISING A THIN FILM OF A NITROGEN-FREE RESINOUS SHEET MATERIAL SOLUBLE IN SULPHURIC ACID. 